Oscillograph galvanometer



mg. 25, 1931. G. L. DIMMICK OSCILLOGRAPH GALVANQMETER Filed Nov. 29. 1929 n 5 e .4 v L. m m .W. m

Patented Au 25, 193i 'sr'rss GLENN L. DIMMICK, OF SCOTIA, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK OSCILLOGRAYH GA LVANOM ETER' Application filed November 29, 1929. Serial No. 410,622.

My invention relates to apparatus including a galvanometer for photographically recording sound on a 'moving' light sensitive member and particularly to the structure of 6 the galvanometer by means of which the exposing light beam is reflected and caused to vibrate in accordance with sound controlled current variations. I

The galvanometer commonly employed heretofore to translate the amplified current vibrations received from the sound pick-up device into vibrations'of the exposing light beam is a standard oscillograph galvanometer forming a part of a well known oscil- 3 lograph in common use for showing wave forms of alternating currents and similar phenomena. This galvanometer has a bifilar construction, namely, has a slender conductor forming a single loop arranged to rotate in the field'ot a permanent magnet and immersed in oil. Attached to the two s1des of the loop is the mirror whose dimensions usually are .017 of an inch Wide by .060 of an inch long. It has long been recognized by those skilled in the art of photographically recording sound that these standard oscillograph galvanometers were for various reasons not as completely adapted to the new use to which they were being put as might be desired. For example, difii-- culty has been encounteredin obtaining on the film suflicient light from the very small mirror with which these galvanometers are provided. The galvanometers, moreover, being of a delicate construction are not well adapted for use by operators who are unskilled in the use of such instruments and where they are liable to receive rough handling or other misuse such as might be ex pected in the case of a portable sound recorder. It is the object of myinvention, therefore, to provide a galvanometer of improved construction by which it' is particularly adapted for use in the recording of sound and by which the difficulties and disadvantages of those instruments heretofore employed are largely, if not completely,

' avoided.

My invention will be better understood from the following description taken in con-,

nection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 shows a common form of optical system including the mirror of my improved galvanometer by which a sound record is photographed on a moving film; Fig. 2 is a full size side view of one embodiment of the galvanometer witha portion of the case broken away; Fig. 3 is a source 6 is concentrated by the condensing lens 7 and lens 8 to a focal point on the mirror 9, a stop 10 being employed to give the desired sharp edge to the light beam directed on the film. From the mirror the light passes on through the cylindrical lens 12 and the spherical lens 13 to the screen 14 having the narrow aperture 15 therein. By means of the microscope objective 16 a reduced image of the aperture is formed on the film and as the mirror is vibrated in accordance with the sound waves illuminating more or less, of the aperture 15 a sound record of the variable width type is produced on the film. It will be understood that the sensitive film is protected by a suitable enclosing casing throughout its passage from the supply magazine to the take-up magazine and that a suitable driving means is provided to move the film at' a uniform speed at the point at which the record is made. For the sake of simplicitythese features have purposely been omitted from the drawings.

The galva'nometer comprising my present invention, which I shall term an oscillograph galvanometer inasmuch as itis adapted to follow all of the high frequency Two pole pieces 23 which are slotted so that each has two pole tips are firmly secured by screws to'the frame in a position to contact with the respective poles of the magnet. For the purpose of clamping the magnet poles against these pole pieces I have pro- F have a slit 38 into which extends a lug 39'on' the end of the armature.

vided .two set screws, one of which is shown at 24, in the frame arranged to engage the magnet.

Between the arms of the magnet and secured to the frame is the armature and coil supporting member 26 whose lower portion has the transverse slot 27 and the bore 28 and whose upper portion comprises the two uprights 29. These are recessed on opposite sides to receive-the disks ,30 each enclosing a coil 31 off many turns of insulated wire and occupying the slots in the pole pieces. The iron armature 32 is fixed atits middle portion to one end of the resilient torsion rod 33, made for example of steel, the other end of which is fixed to the cylinder 34 which is adapted to fit into the bore 28. Tightening of the screws 35 by which the member 26 is attached to the frame serves to firmly clamp the member 34. For damping the free oscillation of the armature two pieces of soft rubber 36 are provided, eachv supported by a plate 37 andheld in position by lugs thereon. The rubber pieces each From the above descrlption it will be seen that the armature has a limited pivotal movement about the was of the-supporting rod 4 The mirror 9 which is vibrated by the armature is plvotally mounted at one side of and separately from the armature and is connected therewith in such a manner that the angle through which it is vibrated is many times that of the armature. The mirror 9 1s shown directly attached to the support 42 which-on one side is rounded and on the otherside is flat with a shallow longitudinal groove therein which receives the knife edge 43 formed on the upper end of plate 44. The armature is connected to the IIllllOI support 42 by the strips 45 which move freely in openings in the pole pieces and which in the present case are shown hav-.

ing those ends adjacent the mirrorunited to form one continuous ribbonor strip which isbent at its middle portion over the curved side of the mirror support 42 and has 1ts ends attached to the ends of the armature. As illustrated the lever arm of the armature is approximately ten times that of the mirror support hence the ratio of the angular deflection of the mirror to that of the armature will be approximately ten.

1 smaller mirrors.

Plate 44 havin the knife edge is shown having two pins 4 which engage in recesses in the frame 20 and constitute a pivotal mount ing for the plate. Screw 48 passing with ampleclearance through the plate 44 serves to retain the plate against accidental displacement which might result in damage to the strips 45 or to the knife 43. By means of the coil spring 49 on screw 50 thestrips 45 are maintained taut and adjustment of the tension is effected by turning the screw 50. In a second plate 52 secured to plate 44 is mounted the small spherical lens 8 forming a part of the optical system. i The two coils 31 are connected together in series with their free terminals connected to the binding posts 53, and operate as a single coil to modify the flux of the magnet in the armature in the well known manner.

While I have shown and described the ple involved in my invention asthe connection may result in various other relations between those members and still produce the advantages which follow from my invention. For maximum mirror deflection per unit torque applied to the armature I have found by calculation that the ratio of transforma tion of the angular movement of the armature to that of the mirror has a definite relation'to the moments of inertia of the armature and mirror. This relation is that the moment of inertia of the armature should equal the product of the moment of inertia of followed closely, a relatively large deflection may be obtained when this relation is only approximately true,- astrict compliance with the above stated rule being necessary only for a condition of maximum mirror deflection for a given torque applied to the armature.

As a result of the construction described above a mirror may. be'employed having an area very much larger than that of the oscillograph galvanometer heretofore employed, for example, a galvanometer ;.which I have constructed of the size shown in Fig. 2 and having a mirror approximately oneeighth of an inch square has substantially the same sensitivity andfrequency characteristic as has been obtained with'the previously used galvanometers with very much The large mirror makes it possible to obtain not only more light on the use of a small mirror in connection with ordinary lenses. Relatively less stray light also results from the use .ofa large mirror because of the larger ratio of silvered surface to the broken edge area. Because of the many turns of the coils 31 as compared with the single turn of the aforementioned galvanometers a much greater torque is applied to the armature; however, by reason of the transformation ratio between armature and mirror movements, the actual movement of the armature is microscopic in magnitude. Hence, although the armature as positioned in the field of the magnet may be in unstable equilibrium, its movements are so extremely slight that any distortional effects produced thereby in the coils are negligible.

My invention is not limited to apparatus including mirror vibrating mechanism having a moving iron armature but is applicable also to apparatus in which the armature of the mechanism is in the form of a moving coil, the term armature being employed in the claims to cover either the moving iron or the moving coil type.

' prising a ma I have chosen the particular embodiment (lBSCIlbGd above as illustrative of my invention and it 'will be apparent that various modifications may be made without departing from the spirit and scope of my invention which modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An oscillograph galvanometer comprising a magnet, an armature member.

mounted for movement in the field thereof, an oscillatable member actuated by said armature member, and connecting means be-' tween the armature member and oscillatable member arranged to produce a greater movement of the latter than that of the former, the moment of inertia ofthe armature member being approximately equal to the product of the moment of inertia of the oscillatable member and. the square of the ratio of sa-idmovements.

2, An oscillograph galvanometer comprising a magnet, an armature mounted to oscillate in the field thereof, an oscillatable memmember including a mirrorspaced from said armature and-an operating connection between said armature and said member, the

lever arm at the armature end of said connection being greater than thelever arm at the oscillatable member end thereof and the total impedance of the moving parts being substantially twice that of the armature alone.

4. An oscillograph galvanometer comprising a magnet, an armature mounted to oscillate in the field thereof, an oscillatable member including a mirror, a bearing for said member, pivotal mounting means for said bearing, a plurality of strips connecting said member with the opposite ends of said armature and arranged to produce a multiplied angular movement of the member, adjustable resilient means for moving said bearing-on its mounting to tension the connecting strips, and means for preventing accidental displacement of said bearing.

5. An oscillograph galvanometer comprising a permanent magnet having pole pieces, and a winding associated therewith, a bar armature mounted to oscillate between said pole pieces, a bearing plate having a knife edge, an oscillatable member, including 'a mirror, engaging said knife edge, ribbons connecting said oscillatable member with said armature, and resilient means engaging said bearing plate for adjustably tensioning said ribbons.

6. An oscillograph galvanometer comprising a permanent magnet having pole pieces and a winding associated therewith, an armature bar, a torsion rod support therefor, an adjustable bearing plate having a knife edge, a mirror support engaging said knife edge, a mirror secured to said support, said polepieces having openings therein, ribbons extending through said openings and engag= ing at opposite ends the armature bar and the mirror support, the length of the lever arm at the armature end of said ribbons being a multiple of the length of the lever arm at the inirror support end thereof, a spring engaging said bearing plate for ten- .sioning said ribbons and a lens holder attached to said bearing plate.

7 An oscillograph'galvanometer comprising a frame, a magnet attached thereto having pole pieces and a winding associated with the pole pieces, an armature bar, a resilient torsion rod fixedly connected at opposite ends respectively with the frame and the armature bar, anadjustable bearing plate, a mirror support having a bearing on said bearing plate, a mirror secured to said support, ribbons connecting the ends of said armature bar with said mirror support and adjusting means engaging thebearing plate for making taut said ribbons and for tensioning said rod.

8. An oscillograph galvanometer comprising a frame, a magnet attached thereto having pole pieces and .a winding associated with the pole pieces, an armature bar, a

resilient torsion rod fixedly connected at opposite ends respectively with the frame and the armature bar, a bearing plate having a pivotal bearing on said ,frame, a mirror support having a knife edge bearing on said plate, a mirror secured to said support, said pole pieces having openings therein, ribbons extending through said openings and con-' necting the ends of said armature bar with said mirror support and a screw for adjusting the bearing plate to tension the ribbons and the resilient torsion rod.

- In witness whereof I have hereunto set my hand this 27th day of November, 1929.

GLENN DIMMIGK. 

